Outline of the project (a detailed description can be foundin the paper „Remote sensing of Carhuarazo volcanic complex" which wassubmitted to Andean Geology on 8th of January 2010)

The video clips show first results of spectral analysis of ASTER reflectance data in a region in southern Peru. The aim was to gain information about alteration zones related to caldera structures by detecting and mapping alteration minerals. Coordinates of the center of the Carhuarazo volcanic complex are 73,7°W and 14,3°S.

The study area in southern Peru encompasses approximately 2,222 km2 at an altitude of 4,000 to 5,000 m. The region is characterized by itsarid climate and therefore sparse vegetation except along river valleys as canbe seen in green colour in the false colour image. In the first step of ourproject we evaluate the capacity of ASTER (Advanced Spaceborn Thermal Emissionand Reflection Radiometer) data aquired on October 18, 2002 for detectingalteration zones and identifying different minerals in this region usinglaboratory spectra from the USGS spectral library and different methods ofmineral and rock detection. Recognizing alteration zones and geologicstructures is very important in large and difficultly accessible areas becauseore deposits are often related to zones of weakness and fluid flow. We areinterested in finding volcanic structures, especially old calderas which are nolonger easily recognized due to erosion and partial cover by younger rocks but maybe the source of large ignimbrite sheets along the western Andean slope.

The video clips show the results of spectral analysis of ASTERreflectance data and a Landsat 7 image using ENVI and ArcGIS with spatialanalyst extension for three dimensional modelling.

Note that calculations were made using USGS spectral library. Of coursemany minerals (especially clay minerals) have very similar spectra in ASTERspectral resolution and there are also variations is spectral propertiesdependent on grain size, trace element content etc. Therefore the obtainedminerals are likely to represent rather a mineral family than just oneparticular mineral. Mapped intensities are relative values and show thepercentage of the signal of a particular mineral contained in the spectra ofeach pixel.

In the future we plan to do extensive fieldwork in the region includingmeasurements of in-situ spectra with an ASD spectrometer as well as analysis ofsamples in order to determine the mineralocical composition. Thus we will beable to calibrate ASTER reflectance data for the application to adjacent scenes.

General aims of the project also include the collection of geochemicaldata and to further extend our ArcGIS data base. Spatial analysis andinterpretation of the different data sets will provide further informationabout probable locations of ignimbrite source regions.

Video Clips:

ASTER false colour image of the research area.

The clip shows the research area as a false colour composite RGB:321. Note that vegetation is shown in bright red colours due to the so called "red edge" in the spectra of plants refering to the region of rapid change in reflectance of chlorophyll in the near infrared range. The false colour image is draped over ASTER DEM with a two fold vertical exaggeration.

PC sharpened Landsat 7 image of the research area showing the spectrally purest pixel of the scene.

The clip shows in a temporal sequence the vegetation mask applied, the results of pixel-purity-index calculation (bright green) and the selected area for matched filtering (for the selection process please refer to the paper text) in yellow.

PC sharpened Landsat 7 image of the research area showing matched filtering results for alunite.

The clip shows in a temporal sequence the results of matched filtering for alunite and kaosmectite. Calculated intensities are displayed in a scale from yellow to red (alunite) and bright green to dark green (kaosmectite: a mixture of kaolinite and smectites) from lower to higher values.

PC sharpened Landsat 7 image of the research area showing matched filtering results for nacrite.

The clip shows in a temporal sequence the results of matched filtering for nacrite and recforite. Calculated intensities are displayed in a scale from dark blue to bright blue (recforite) and yellow to red (nacrite) from lower to higher values.

PC sharpened Landsat 7 image of the research area showing matched filtering results for dickite.

The clip shows in a temporal sequence the results of matched filtering for kaolinite and dickite. Calculated intensities are displayed in a scale from bright blue to dark blue (kaolinite) and dark green to bright green (dickite) from lower to higher values.

PC sharpened Landsat 7 image of the research area showing matched filtering results for eugsterite.

The clip shows in a temporal sequence the results of matched filtering for eugsterite and natrolite. Calculated intensities are displayed in a scale trom dark blue to bright blue (natrolite) and yellow to red (eugsterite) from lower to higher values.